1. Field of the Invention
The present invention relates to an industrial two-layer fabric having a warp binding yarn, in particular, an industrial two-layer fabric featuring reduced internal abrasion, less dehydration marks, and excellent surface smoothness.
2. Background Art
Industrial fabrics obtained by weaving warps and wefts have conventionally been used widely. They have been used as, for example, papermaking fabrics, conveyor belts, and filter cloths and required to have fabric characteristics suited for intended uses or using environments, respectively. Of such fabrics, papermaking fabrics used in a papermaking step to dehydrate raw materials by making use of the screen of the fabrics should satisfy a severe demand. There is therefore a demand for the development of, for example, fabrics which are excellent in surface smoothness and therefore do not transfer a dehydration mark of the fabrics to paper; or fabrics having a dehydration property which permits sufficient and uniform removal of extra water contained in the raw materials, having enough rigidity and abrasion resistance to enable desirable use of them even under severe environments, and further capable of maintaining conditions necessary for making good paper for a prolonged period of time. In addition, papermaking fabrics have been required to have a fiber supporting property, an improved paper making yield, dimensional stability, running stability, and the like. Further, due to the speed-up of a paper making machine in recent years, requirements for papermaking fabrics become more severe.
Demands for most of the existing industrial fabrics and solutions thereof can be understood from a description on papermaking fabrics on which the most severe demand is imposed among industrial fabrics. Therefore, a description will next be made with papermaking fabrics as an example.
It is known that while an industrial two-layer fabric obtained by bringing together an upper side fabric and a lower side fabric with a binding yarn travels on a papermaking machine, there occurs abrasion at a position where the upper side fabric is brought into contact with the lower side fabric.
Particularly, with a recent increase in the speed of a papermaking machine, internal abrasion occurs more frequently. The internal abrasion causes fluffing of the surface of the yarns inside the fabric and this deteriorates the airflow degree of the mesh, resulting in reduction in dehydration rate.
As a method of preventing such internal abrasion, there is known a method of enhancing adhesion between an upper side fabric and a lower side fabric. As a method of enhancing adhesion between an upper side fabric and a lower side fabric, there is, for example, a method of widening the diameter of binding yarns or increasing the number of binding yarns (refer to Japanese Patent Laid-Open No. 2001-98483). For example, by increasing the number of binding yarns and thereby increasing a binding ratio in a complete design or a repeating unit of a fabric, improvement in adhesion can be achieved due to an increase in the number of yarns binding an upper side fabric and a lower side fabric.
When the binding ratio is increased by the above-mentioned method, however, a dehydration mark is likely to appear in the upper side fabric. This means that an industrial two-layer fabric that includes a warp binding yarn has conventionally a structure in which an upper side warp does not form a knuckle on an upper side fabric at a site where it is supposed to form and, instead, a lower side warp (a binding yarn) forms a knuckle on the upper side fabric (refer to Japanese Patent Laid-Open No. 2003-342889). At such a site where the knuckle of an upper side warp is made up for by the lower side warp, a substantial warp density doubles in the upper side because of the presence of the upper side warp which is out of the original arrangement. When the warp density increases at a site, the site becomes a dehydration inhibition site. When the number of binding yarns is increased and thereby a binding ratio is increased in a fabric having such a structure, the resulting fabric has uniformly-arranged dehydration inhibition sites. These sites constitute a dehydration inhibition line depending on the arrangement shape of the dehydration inhibition sites. As a result, paper made using such a fabric has on the surface thereof dehydration marks.
In order to prevent an increase in the density of dehydration inhibition sites due to binding yarns, there may be a method of increasing the number of wefts in the complete design or the repeating unit and thereby lengthening the long longitudinal direction in the complete design. Such a structure can reduce the density of the dehydration inhibition sites. On the other hand, when such a structure is employed for a conventional design, one binding yarn continuously forms a plurality of knuckles on an upper side fabric.
It is known that in a design in which one binding yarn continuously forms a plurality of knuckles on an upper side fabric, the resulting fabric has a convex shape with the center of the continuous knuckles as a peak.
For example, in FIG. 1A, a warp (binding yarn) 1 passes over a weft 1′, passes under a weft 2′ and passes over a weft 3′ and forms knuckles on an upper side fabric at the wefts 1′ and 3′. In such a weave structure, a stress is applied to the fabric according to the tension of the warp (binding yarn) 1 in a direction of an arrow so that a convex shape with the weft 2′ located at the center position as a peak is formed. In FIG. 1B, a warp (binding yarn) 2 passes over wefts 1′ and 2′, under wefts 3′ and 4′, over wefts 5′ and 6′, under wefts 7′ and 8′ and over wefts 9′ and 10′ and forms knuckles on an upper side fabric at wefts 1′ and 2′, 5′ and 6′ and 9′ and 10′. In such a weave structure, a stress is applied to the fabric according to the tension of the warp (binding yarn) 2 in a direction of the arrows so that a convex shape with wefts 5′ and 6′ located at the center portion as a peak is formed. Further, in FIG. 1C, a warp (binding yarn) 3 passes over wefts 1′, 5′, 9′, and 13′ and passes under other wefts and forms a knuckle on an upper side fabric at the wefts 1′, 5′, 9′, and 13′. In such a weave structure, a stress is applied to the fabric according to the tension of the warp (binding yarn) 3 in a direction of the arrows so that a convex shape with the weft 7′ and the neighboring wefts located at the center position as a peak is formed.
Uniform arrangement of convex sites as described above becomes a cause of not only dehydration marks but also a cause of deteriorating the surface smoothness of the fabric.
The existing industrial two-layer fabrics have the above-mentioned problems, but these problems can be overcome by decreasing a binding ratio. Decreasing a binding ratio, however, deteriorates the adhesion between an upper side fabric and a lower side fabric as described above and thereby causes internal abrasion. This suggests that there is a trade-off relationship between a binding ratio and adhesion.
There has been no design capable of satisfying all the required characteristics such as internal abrasion, dehydration mark, and surface smoothness.